1) Do you have an 'example App' that we can download to look at how your PDF Viewer looks & feels like? an alternative, would be to have an example App from one of your customers? we would need it in the 3 platforms. Androd, iOS and UWP.
2) How much can we customize & brand (change the look & feel) of the PDF reader when used in an App? can we use our Icons, colors and font? (maybe even items positioning)
3) Do you allow reproduction of Youtube videos (directly streamed from Youtube) inside of your PDF Reader?
Yes we have full example project in our SDK download, including a viewer sample project, that is ready to go.
We also have a showcase app in all the mobile stores. This is completely free. www.xodo.com
While Xodo has extra features not included in the SDK samples, such as integration into some 3rd party cloud storage solutions, the core of it is what you get out of the box with our SDK sample.
You have an incredible amount of flexibility to customize the viewer. All of the user experience logic/code is provided to you in the SDK, under the PDFViewCtrlTools project. This forum is full of answers to people asking how to make various customizations to the user interface.